Wait on Notification with Notifier History Function

LabVIEW 2018 Help


Edition Date: March 2018
Part Number: 371361R-01
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Owning Palette: Advanced Notifier Waiting Functions

Requires: Base Development System

Waits until a notifier receives a message. This function tracks the most recent message and timestamp for each individual notifier when you use this function repeatedly with different notifiers.

Details  

notifier is a reference to a notifier. Use the Obtain Notifier function to obtain a notifier reference.
ignore previous indicates whether to ignore messages that LabVIEW sends to the notifier before it calls this function. If TRUE and the notifier contains a message before you call this function, this function waits until the notifier receives another message. If FALSE (default) and the notifier contains a message before you call this function, this function continues to execute.
timeout in ms specifies the time, in milliseconds, that the function waits for the notifier to receive a message. The default is –1, which indicates never to time out.

If the function waits timeout in ms and the notifier does not receive a message, timed out? is TRUE.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
notifier out returns notifier unchanged.
notification is the last message the notifier receives. This data type changes to match the subtype of notifier.
timed out? is TRUE if the notifier does not receive a message before the function times out or if an error occurs.
error out contains error information. This output provides standard error out functionality.

Wait on Notification with Notifier History Details

Each unique instance of this function remembers the timestamp of the most recent message that each individual notifier receives.

Maintaining notifier history prevents dropped messages and other problems when you use this function repeatedly with different notifiers. When the notifier receives a message, this function continues to execute. Use the Send Notification function to send the message. If a notifier reference becomes invalid when another function closes it, the function stops waiting and returns error code 1122. If the notifier does not contain a message, this function waits until the notifier receives a message.

Maintaining notifier history also causes this function to run slower than the Wait on Notification function. The Wait on Notification function does not maintain notifier history and might experience deadlock when you use it repeatedly with different notifiers.

Use the Wait on Notification from Multiple with Notifier History function to handle an array of notifier references.

If ignore previous is FALSE, each instance of the Wait on Notification with Notifier History function waits if it has not received notification. The function also waits if the timestamp of the current message is the same as when the instance of the function last executed. If the message is new, then the function returns the message.

If ignore previous is TRUE, the Wait on Notification with Notifier History function always waits for a new message, even if the message currently in the notifier is one the function has never seen before.

This function does not remove the message from the notifier. Although a single instance of the function returns a message only once, other instances of the function or the Wait on Notification from Multiple function repeat the message until you call the Send Notification function with a new message.

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